With the advance of display technologies and the progress in state of the art, various display apparatuses comprising delicate handheld displays, high-definition display screens, and three-dimensional (3D) displays achieving visual effects as real as possible have been developed, and images vividly displayed by these display apparatuses reproduce lifelike experiences of excitement beyond imagination. Among the display apparatuses, a head mount display (HMD) characterized by convenience of use and privacy protection has drawn attention to the field of the display technologies. In general, a virtual image produced by the existing HMD is approximately 2 meters to 10 meters away from a human eye, and the field of view is about 22 degrees, such that the existing HMD is not apt to interact with a user in an intuitive manner. In addition, the existing HMD employs optical components with large dimensions in order to eliminate image aberration when images are displayed and observed at a wide viewing angle. Thereby, the large volume and the significant weight of the HMD are very much likely to discomfort the user. Moreover, it is rather difficult to adjust the limited focal lengths and shapes of optical components in the HMD for different users. As a result, how to ensure the compactness as well as the wide display viewing angle of the HMD and simultaneously allow the user to interact with the HMD and enjoy the convenience of use of the HMD has become one of the issues to be resolved promptly in the field of the display technologies.